This invention relates to the field of can end lining compounds, and, more particularly, to a method of removing water from water base can end lining compounds after the can ends have been lined.
The art of container sealing has an established terminology which will be used in this specification. The walls of the container are known as the "body". The end closures are known as "ends". The gasket which is interposed between the ends and body and is responsible for the hermetic or liquid-tight seal between the parts is known as the "lining". The plastic or liquid composition which, upon cooling or drying, forms the solid gasket, is known as "lining".
The body of the can is a cylindrical piece of sheet metal normally made by forming a rectangular piece of metal and then joining the ends of the rectangle along the side seam. The metal in the ends of the cylinder are flanged outwardly. The can is completed by placing a circular piece of metal called the "end" over each end of the cylinder and rolling the outer edge of the end and flange on the body together in a double seam. That portion of the end which covers the interior of the can is called the "panel". The outer periphery of the end is formed into a circular depression called the "channel" which cooperates with the flange on either end of the body. The outer edge of the channel called the "curl" is deformed upwardly and inwardly to provide contact of the can end with the inner side of the flange of the can body during the first stage of the double seaming operation. The inner wall of the channel, i.e., the portion between the channel and the panel, is known as the "shoulder". The plastic or liquid composition which forms the "lining" is placed in the channel of the can end.
Sealing compounds for can covers ("ends") are commonly applied to the covers in liquid form. The machines, called "lining machines", which apply the compound to the joint area, have, as essential operating elements, a continuously rotating chuck which receives and rotates the end, a "nozzle", essentially a squirt gun, controlled by a needle valve which projects the compound downwardly onto the joint area of the end, and a quick opening and closing cam which lifts the needle valve and closes it at the proper instant. Through the operation of the lining machine, a ring of fluid compound is formed on the joint area adjacent the periphery of the end. This ring of compound, whether in liquid form or later when it is dried, or fluxed into a solid mass is called the "lining". Its function is to form the gasket between the can parts and hermetically seal the can.
A common type of compound-applying ("lining") machine removes a blank end from a stack; slides the end along a table; places it on a continuously revolving chuck, where the compound is applied and placed; pushes the end from the chuck; tucks it beneath a stack of finished ends; and places a new end on the chuck in a single cycle of operation. After the can ends have been lined, they are conveyed to an area where the volatile components of the lining composition are removed.
Ballou, et al, U.S. Pat. No. 3,013,896 and Flaherty, U.S. Pat. No. 3,310,196 describe the basic operations employed in lining can ends and attaching the can ends to the can body. These references are incorporated by reference in this application to the extent not provided for herein.
Water base can end lining compounds are water dispersions of special rubbers which, when flowed into can ends and dried, provide an hermetic seal. The solids portion of a water base can end lining compound ranges from about 40 percent to about 75 percent of the total composition. The water portion of the compound ranges from 25 percent to 60 percent of the total composition. Based upon 100 parts per hundred of rubber (hereinafter referred to as phr), the solids portion of a typical water base lining compound has the following composition (all parts are expressed in weight):
______________________________________ Ingredient Amount ______________________________________ Rubber 100 phr Pigment and/or filler 50-200 phr Resin 0-100 phr Antioxidant less than 1% Bacteriocide less than 1% Surface Active Agents 0.5% to 10% ______________________________________
The conventional method of drying the water base compounds involves the use of an oven dryer.
Water base compounds must be thoroughly dried in the can end after being applied, or squeezing may result if the ends are double seamed before the compound is completely dry. Temperature and time of drying are variable depending upon the type of dryer and arrangement of the can ends in the dryer. When the can ends are stacked on top of one another and placed in an oven in stacks, usually a 20-minute cycle at 200.degree. F. to 250.degree. F. will give best results. When the lined can ends are dried in a helical stacker oven wherein they are separated from one another, 8-10 minutes at 190.degree. F. to 210.degree. F. is usually sufficient. The most efficient dryers are gas or electric-fired, forced draft ovens which employ the principle of recirculating air.
A 24-48 hour aging period is advised for lined ends in order for the compounds to establish a moisture equilibrium and to insure best performance. This also allows for adjustment in rheological properties due to the drastic change from dispersion to solidified gasket material.
A serious problem with the conventional drying method is that numerous can makers do not possess the facilities for setting up oven driers of sufficient capacity to be economically feasible. This problem came about because can makers generally preferred to use solvent base can end lining compounds. Solvent base can end lining compounds are primarily solvent solutions of special rubber. Ends lined with solvent base compounds can be dried without heat, but should be dried in an area where there is a good air circulating and exhaust system.
Because of increased awareness of health problems which may be due in part to organic solvents which originate from can end lining compounds, can makers and canners now prefer to employ water base can sealing compounds. The problem of removal of water from the applied compound without the use of oven dryers must now be addressed.
To achieve commercial acceptance, an "air dry" waterbase can sealing compound must dry (i.e., be seamable) within a maximum of 24 hours after lining onto can ends under a wide range of ambient atmospheric conditions. The sealing compounds which have been formulated to date are generally lined at 60%-75% total solids (by weight) and must be dried to approximately 97% total solids (by weight) before they can be subjected to double seaming without squeezing out of the seam. Even allowing for technical progress in formulating compounds which can be lined at higher total solids and/or exhibit increased squeeze resistance at lower total solids, it is expected that waterbase compounds will have a considerable amount of water to be evaporated within the 24 hour time period.
Accordingly, it is an object of this invention to provide a method for removal of water from water base can end lining compounds after application without the use of an oven dryer or other source of heat.
It is another object of this invention to reduce the energy requirements of the process employed in lining can ends with water base can end lining compounds.